The state of the art can be defined by various patents. All these patents describe means to vary the flexibility or stiffness as a function of the load of the vehicle. Other patents describe tilt correctors. These patents cause the intervention upon application of energy, of a mechanism which modifies the stiffness or the flexibility as a function of the load. Certain patents modify the stiffness or the flexibility as a function of the choice of driving mode (example: sports mode, family mode, etc. . . . ) By applying energy, the flexibility of the elastic elements can vary as a function of detectors (of direction, tilt, speed, etc. . . . ) The change of flexibility or of stiffness is applicable throughout the suspension.
In the very great majority of cases, the suspensions of automobiles are constituted by a combined "spring+shock absorber" giving rise, at the level of the vehicle wheel, to a suspension force which increases in a constant manner with the collapse of the suspension. In other words, the stiffness or flexibility is constant (stiffness=delta F over delta L or a variation of force over variation of length), and this regardless of the nature of the spring used (the elastic element could be a helicoidal metal spring, a torsion blade or blades, or pneumatic, etc. . . . )
Nevertheless there are suspensions in which this stiffness varies as the load on the vehicle wheel. These suspensions are of so-called variable flexibility and all those known to the present rely on increase in stiffness upon increase of load on the vehicle wheel; this increase of stiffness is adapted better to control the maintenance of the "increased" mass of the vehicle. It can be obtained in various ways:
according to the oldest system (leaf springs), the curvature of the leaves may be adapted so that they act progressively; PA1 in a helicoidal spring, in the same way, the pitch of the turns may be progressive so that these latter come into contact with each other one after the other during collapse; PA1 in a helicoidal spring, there can also be different zones each of constant pitch, but of different values. The first part collapses until the turns touch, while only the second part continues to be compressed; this gives rise to two successive stiffnesses, the greater being at the end of collapse; PA1 by kinematic bias, the stiffness at the level of the wheel can also be made to vary by varying the multiplication ratio relative to the spring; PA1 in an oleopneumatic suspension, the volume of gas diminishes in the accumulator of the element giving rise to a variation of this volume which is more and more abrupt, from which the stiffness increases. PA1 1. A portion of the length of the spring bar can be placed out of service, only the remainder of the length acting as a spring; PA1 2. At an appropriate point along the torsion bar is fixed an arm which, in torsion, bears on an abutment whose position relative to the arm can be changed as desired; PA1 3. The abutment is provided in the form of a rotatable non-circular disk on the periphery of which comes to bear the arm of the torsion bar; PA1 4. On the periphery of the disk are provided graduations determining the various positions of rotation of the arm of the torsion bar.
In these different well known examples, the stiffness always increases with collapse of the suspension. This increase of stiffness is ordinarily progressive.
The state of the art may be defined by the following patents:
FR-A-1.349.851: Suspension of a movable engine comprising one or several elements of usual deformable means, such as springs or other devices which can if desired be complex and buffered, acting either by contraction or extension or torsion of their filaments, materials or elastic fluids, so arranged that:
their elongation and corresponding charge may be different from those of subsequent expanders, namely predetermined within limits of loads defined or above an occasional predetermined surcharge;
the combination of the elastic elements permits any obstacle acting on one of these elements to provoke non-resonance of the engine below this obstacle and to benefit from the flexibility of several, that is, the assembly of the elements, that these adjustments and connections may be maintained within limits defined by a given surcharge or discharge at rest, namely a lower guard (or in the plane of displacement) of this engine.
This patent directs all its efforts to achieve non-resonance. Nothing is described which suggests the positioning and the value of the different regions of stiffness.
U.S. Pat. No. 3,559,976: this patent discloses an assembly of several springs permitting obtention of several stiffnesses. The springs are mounted in series and act in the same direction. Beyond a certain path during increase of the load, one of the springs is eliminated.
This operation is completely different from that of the process according to the invention.
FR-A-1.212.305: improvements in shock absorbers particularly characterized by the use of two springs, one for support, the other for reaction, and such that the characteristic of the assembly will not be linear, the resistance to vibrations increasing as the amplitude of these latter. When the load is applied, it is essential that the oppositely acting spring be non-compressed, but in a condition such that it can oppose an increasing resistance to the dynamic flexure, consecutively to the action of the vibratory forces which comprise it.
The concept of non-resonance seems ideal in this mounting adapted not to a vehicle suspension but to elastic pads for the maintenance of compressors or mechanisms of fixed machines, in which the movements to be absorbed are of constant or progressively variable frequency. The stiffness increases therefore rapidly and symmetrically about the point of static equilibrium, so as to "muzzle" any reaction arising from displacements of the mass (for example, the unbalance due to poor loading of a washing machine).
FR-A-809.336: torsional suspension, particularly for oscillating half spindles, characterized by one or several of the following features, taken separately or in combination:
The operation is quite different from that of the suspension according to the invention because it again is a matter of the classic principle of increase of stiffness during increase of load on the vehicle (principle of classic suspension with variable flexibility).
BE-A-522.734: the novelty of the invention consists in that the chamber or low pressure space is placed above the piston of the shock absorber and in that the compensation chamber begins directly above the level of the oil. According to this arrangement, the high pressure space is located below the piston and is limited downwardly by the guides and the sealing means of the piston rod. It thus results, in contrast with the known shock absorber systems, that the high pressure space in the case of small losses of shock absorber liquid which otherwise immediately upset the operation, is not influenced by these losses, for example of oil, and as a result the high pressure path as well as the principal function of a shock absorber retains its full working capacity even in case of oil losses.
It thus concerns above all a shock absorber for a motorcycle suspension. In complement of the shock absorber (purely hydraulic), a spring installed about the shock absorber portion has been replaced by two springs of different stiffness, so as to obtain "increasing hardness" to avoid flattening of the suspension. It therefore is a matter of a "classic suspension with variable flexibility". A small spring, disposed in the shock absorber itself, is adapted to cushion the end of extension movement.
DE-A-2.043.512: elastic system for automotive vehicles, with springs, disposed one behind the other, supporting the vehicle body and with a blocking device for blocking one or several springs relative to the vehicle body, a detector measuring the speed of oscillation of the mass of the vehicle body being provided to actuate the blocking device, which "opens" periodically the blocking device when the speed of oscillation attains the value zero (point of reversal of the oscillation) and closes it after a half oscillation of two springs between which there is exerted the action of the blocking device (according to patent application P.1928 961.3 and DE 2 043 512), characterized by the fact that the hydraulic portions of the springs provided in the form of elastic oleopneumatic elements are connected by hydraulic connections and that the blocking device comprises the combination of valves to block or free the circulation of liquid, or even a blockable piston floating freely in the chamber under pressure of the hydraulic portion.
The elastic elements (hydropneumatic) are not mounted in opposition, but "disposed one behind the other" (or in parallel). There is a change of stiffness by neutralization of one of the elastic elements upon information received from a detector measuring the speed of oscillation of the vehicle body.